Well, Overall, Id Have To Say gengar. Heres why:
Special Sweeping, Huge Move Pool, Amazing SA and Speed so Great Sweeping Stats, Not a Bad Typing. Original. OU. Popular. Cool Looking. Levitate. What More Could Ya Want?
Thunderbolt: Gyrados, Who Needs Electric types when you can have Gengar???
Shadow Ball: STAB Owns.
Sludge Bomb/Energy Ball: Special STAB. Or Coverage.
Focus Blast: Bye Tyranitars.
Mismagius: Meh, overall, a regular Ghost Type. Not Original, Not as cool looking. Still Great Movepool. Even better than Gengars. Great Special Tank with Calm Mind.
Calm Mind: Special Tank.
Shadow Ball: STAB For The Win.
Thunderbolt/Energy Ball/Psychic: Coverage.
Psychic/Thunedrbolt/Energy Ball: More other coverage.